GREEN/TRAN and all,
Yes, the approval letter they mention in I-485 is in fact your NOA2 from the I-129F's days... seem so long agon, doesn't it?

Just make a photo copy and mail it in, keep your original for the Interview, if you get one
Remember, this is once again, make you really think the big picture. They want to match up your very first stage: I-129 to Visa to GC. However at GC stage, they want to once again, make absolutely sure they issue the GC to the right person, for the right kind and right reason (i.e. 2-yrs conditional GC)
Good luck with your filing and speedy approval.
chuck and kim